Preparation of a robust immobilized biocatalyst of β-1,4-endoxylanase by surface coating with polymers for production of xylooligosaccharides from different xylan sources

Topochemical Design of Cellulose-Based Carriers for Immobilization of Endoxylanase

Xylooligosaccharides (XOSs) gained much attention for their use in food and animal feed, attributed to their prebiotic function. These short-chained carbohydrates can be enzymatically produced from xylan, one of the most prevalent forms of hemicellulose. In this work, endo-1,4-β-xylanase from Thermotoga maritima was immobilized on cellulose-based beads with the goal of producing xylooligosaccharides with degrees of polymerization (DPs) in the range of 4-6 monomeric units. More specifically, the impact of different spacer arms, tethers connecting the enzyme with the particle, on the expressed enzymatic activity and oligosaccharide yield was investigated. After surface functionalization of the cellulose beads, the presence of amines was confirmed with time of flight secondary ion mass spectrometry (TOF-SIMS), and the influence of different spacer arms on xylanase activity was established. Furthermore, XOSs (DPs 2-6) with up to 58.27 mg/g xylan were obtained, which were greatly enriched in longer oligosaccharides. Approximately 80% of these XOSs displayed DPs between 4 and 6. These findings highlight the importance of topochemical engineering of carriers to influence enzyme activity, and the work puts forward an enzymatic system focusing on the production of longer xylooligosaccharides.

Immobilization and Application of the Recombinant Xylanase GH10 of Malbranchea pulchella in the Production of Xylooligosaccharides from Hydrothermal Liquor of the Eucalyptus (Eucalyptus grandis) Wood Chips

Xylooligosaccharides (XOS) are widely used in the food industry as prebiotic components. XOS with high purity are required for practical prebiotic function and other biological benefits, such as antioxidant and inflammatory properties. In this work, we immobilized the recombinant endo-1,4-β-xylanase of Malbranchea pulchella (MpXyn10) in various chemical supports and evaluated its potential to produce xylooligosaccharides (XOS) from hydrothermal liquor of eucalyptus wood chips. Values >90% of immobilization yields were achieved from amino-activated supports for 120 min. The highest recovery values were found on Purolite (142%) and MANAE-MpXyn10 (137%) derivatives, which maintained more than 90% residual activity for 24 h at 70 °C, while the free-MpXyn10 maintained only 11%. In addition, active MpXyn10 derivatives were stable in the range of pH 4.0−6.0 and the presence of the furfural and HMF compounds. MpXyn10 derivatives were tested to produce XOS from xylan of various sources. Maximum values were observed for birchwood xylan at 8.6 mg mL−1 and wheat arabinoxylan at 8.9 mg mL−1, using Purolite-MpXyn10. Its derivative was also successfully applied in the hydrolysis of soluble xylan present in hydrothermal liquor, with 0.9 mg mL−1 of XOS after 3 h at 50 °C. This derivative maintained more than 80% XOS yield after six cycles of the assay. The results obtained provide a basis for the application of immobilized MpXyn10 to produce XOS with high purity and other high-value-added products in the lignocellulosic biorefinery field.

Xylooligosaccharides Production from Xylan Hydrolysis Using Recyclable Strong Acidic Cationic Exchange Resin as Solid Acid Catalyst

As the emerging functional food additives, xylooligosaccharides are receiving high commercial interest due to their excellent gut microbiota modulation capacity, and accumulating studies have suggested that acidic hydrolysis for xylooligosaccharides preparation is the most convenient and cost-effective approach, whereas liquid acids are still limited due to the challenges in acid catalysts separation and products recovery. In the present study, a strong acidic cationic resin (NKC-9), as a recyclable solid acid catalyst, was successfully applied to xylooligosaccharides production by acidic hydrolysis of xylan. Additionally, a central composite design with response surface methodology was employed to optimize the conditions for maximizing xylooligosaccharides yields. The results suggested that xylooligosaccharides with the desired degree of polymerization (2-6) could be prepared, and the maximum yield was reached 47.7% in the case of 5% solid acid loading at 131 °C for 42 min. Finally, the recyclability of the solid acid catalysts confirmed that it was a cost-effective strategy for xylooligosaccharides production.

Omega-3 production by fish oil hydrolysis using a lipase from Burkholderia gladioli BRM58833 immobilized and stabilized by post-immobilization techniques

Immobilization of lipase from Burkholderia gladioli BRM58833 on octyl sepharose (OCT) resulted in catalysts with higher activity and stability. Following, strategies were studied to further stabilize and secure the enzyme to the support using functionalized polymers, like polyethylenimine (PEI) and aldehyde-dextran (DEXa), to cover the catalyst with layers at different combinations. Alternatively, the construction of a bifunctional layer was studied using methoxypolyethylene glycol amine (NH 2 -PEG) and glycine. The catalyst OCT-PEI-DEXa was the most thermostable, with a 263.8-fold increase in stability when compared to the control condition. When evaluated under alkaline conditions, OCT-DEXa-PEG 10 /Gly was the most stable, reaching stability 70.1 times greater than the control condition. Proportionally, the stabilization obtained for B. gladioli BRM58833 lipase was superior to that obtained for the commercial B. cepacia lipase. Preliminary results in the hydrolysis of fish oil demonstrated the potential of the coating technique with bifunctional polymers, resulting in a stable catalyst with greater catalytic capacity for the production of omega-3 PUFAs. According to the results obtained, it is possible to modulate B. gladioli BRM58833 lipase properties like stability and catalytic activity for enrichment of omega-3 fatty acids.

Stabilization of enzymes via immobilization: Multipoint covalent attachment and other stabilization strategies

The use of enzymes in industrial processes requires the improvement of their features in many instances. Enzyme immobilization, a requirement to facilitate the recovery and reuse of these water-soluble catalysts, is one of the tools that researchers may utilize to improve many of their properties. This review is focused on how enzyme immobilization may improve enzyme stability. Starting from the stabilization effects that an enzyme may experience by the mere fact of being inside a solid particle, we detail other possibilities to stabilize enzymes: generation of favorable enzyme environments, prevention of enzyme subunit dissociation in multimeric enzymes, generation of more stable enzyme conformations, or enzyme rigidification via multipoint covalent attachment. In this last point, we will discuss the features of an "ideal" immobilization protocol to maximize the intensity of the enzyme-support interactions. The most interesting active groups in the support (glutaraldehyde, epoxide, glyoxyl and vinyl sulfone) will be also presented, discussing their main properties and uses. Some instances in which the number of enzyme-support bonds is not directly related to a higher stabilization will be also presented. Finally, the possibility of coupling site-directed mutagenesis or chemical modification to get a more intense multipoint covalent immobilization will be discussed.

Xylo-Oligosaccharides, Preparation and Application to Human and Animal Health: A Review

Xylo-oligosaccharides (XOS) are considered as functional oligosaccharides and have great prebiotic potential. XOS are the degraded products of xylan prepared via chemical, physical or enzymatic degradation. They are mainly composed of xylose units linked by β-1, 4 bonds. XOS not only exhibit some specific physicochemical properties such as excellent water solubility and high temperature resistance, but also have a variety of functional biological activities including anti-inflammation, antioxidative, antitumor, antimicrobial properties and so on. Numerous studies have revealed in the recent decades that XOS can be applied to many food and feed products and exert their nutritional benefits. XOS have also been demonstrated to reduce the occurrence of human health-related diseases, improve the growth and resistance to diseases of animals. These effects open a new perspective on XOS potential applications for human consumption and animal production. Herein, this review aims to provide a general overview of preparation methods for XOS, and will also discuss the current application of XOS to human and animal health field.

Functionalization of Porous Cellulose with Glyoxyl Groups as a Carrier for Enzyme Immobilization and Stabilization

The functionalization of the internal surface of macroporous carriers with glyoxyl groups has proven to highly stabilize a large variety of enzymes through multipoint covalent immobilization. In this work, we have translated the surface chemistry developed for the fabrication of glyoxyl-agarose carriers to macroporous cellulose (CEL). To that aim, CEL-based microbeads were functionalized with glyoxyl groups through a stepwise alkoxylation (or alkylation)/oxidation synthetic scheme. This functionalization sequence was analyzed by solid-state NMR, while the scanning electron miscroscopy of CEL microbeads reveals that the mild oxidation conditions negligibly affect the morphological properties of the material. Through the optimal functionalization protocol using rac-glycidol, we introduce up to 200 μmols of aldehyde groups per gram of wet CEL, a similar density to the one obtained for the benchmarked agarose-glyoxyl carrier. This novel CEL-based carrier succeeds to immobilize and stabilize industrially relevant enzymes such as d-amino acid oxidase from Trigonopsis variabilis and xylanases from Trichoderma reseei. Remarkably, the xylanases immobilized on the optimal CEL-based materials present a half-life time of 51 h at 60 °C and convert up to 90% of the xylan after four operation cycles for the synthesis of xylooligosaccharides.

The optimization of fermentation conditions for Pichia pastoris GS115 producing recombinant xylanase

Xylanase is a member of an important family of enzymes that has been used in many biotechnological processes. However, the overall cost of enzyme production has been the main problem in the industrial application of enzymes. To obtain maximum xylanase production, statistical approaches based on the Plackett-Burman design and response surface methodology were employed. The results of the statistical analyses demonstrated that the optimal conditions for increased xylanase production were the following: inoculum size, 3.8%; maize meal, 4.5%; histidine, 0.6%; methanol, 1%; culture volume, 20%; bean pulp, 30 g L-1; and Tween-80, 0.8%; and pH 5.0. Verification of the optimization demonstrated that 3273 U mL-1 xylanase was observed under the optimal conditions in shake flask experiments. SDS-PAGE results showed that the size of xylanase protein was about 23 kDa. The results showed that the xylanase produced by fermentation came from Aspergillus Niger by MALDI-TOF-MS. The optimized medium resulted in 2.1- and 1.4-fold higher the activity of xylanase compared with the unoptimized medium (the main nutrients are maize meal and bean pulp) and laboratory medium (the main nutrients are yeast extract and peptone), respectively. The optimization of fermentation conditions is an effective means to reduce production cost and improve xylanase activity.

Designing continuous flow reaction of xylan hydrolysis for xylooligosaccharides production in packed-bed reactors using xylanase immobilized on methacrylic polymer-based supports

The present study focuses on the development and optimization of a packed-bed reactor (PBR) for continuous production of xylooligosaccharides (XOS) from xylan. For this purpose, three different methacrylic polymer-based supports (Relizyme R403/S, Purolite P8204F and Purolite P8215F) activated with glyoxyl groups were morphologically characterized and screened for the multipoint covalent immobilization of a xylanase. Based on its physical and mechanical properties, maximum protein loading and thermal stability, Relizyme R403/S was selected to set up a PRB for continuous production of XOS from corncob xylan. The specific productivity for XOS at 10 mL/min flow rate was 3277 g_XOS g_enzyme^-1 h^-1 with a PBR. This PBR conserved >90% of its initial activity after 120 h of continuous operation.

Stabilization of Enzymes by Multipoint Covalent Attachment on Aldehyde-Supports: 2-Picoline Borane as an Alternative Reducing Agent

Enzyme immobilization by multipoint covalent attachment on supports activated with aliphatic aldehyde groups (e.g., glyoxyl agarose) has proven to be an excellent immobilization technique for enzyme stabilization. Borohydride reduction of immobilized enzymes is necessary to convert enzyme–support linkages into stable secondary amino groups and to convert the remaining aldehyde groups on the support into hydroxy groups. However, the use of borohydride can adversely affect the structure–activity of some immobilized enzymes. For this reason, 2-picoline borane is proposed here as an alternative milder reducing agent, especially, for those enzymes sensitive to borohydride reduction. The immobilization-stabilization parameters of five enzymes from different sources and nature (from monomeric to multimeric enzymes) were compared with those obtained by conventional methodology. The most interesting results were obtained for bacterial (R)-mandelate dehydrogenase (ManDH). Immobilized ManDH reduced with borohydride almost completely lost its catalytic activity (1.5% of expressed activity). In contrast, using 2-picoline borane and blocking the remaining aldehyde groups on the support with glycine allowed for a conjugate with a significant activity of 19.5%. This improved biocatalyst was 357-fold more stable than the soluble enzyme at 50 °C and pH 7. The results show that this alternative methodology can lead to more stable and active biocatalysts.